As an example of devices for discharging liquid materials, there is known a device that a shaft member being rotatable or movable forward and backward is disposed in a flow passage extending from a supply port to which the liquid material is supplied, to a discharge port from which the liquid material is discharged, and that the liquid material is discharged from the discharge port with the operation of the shaft member (see, e.g., Patent Document 1).
In the device disclosed in FIG. 1 of Patent Document 1, a liquid material stored in a syringe is introduced to a flow passage, which is formed in a housing of a distributor, through a hole, and the liquid material is discharged from a nozzle with forward movement of a shaft. Here, the shaft is inserted in a flow bore, and the flow passage is formed by a gap between the flow bore and the shaft inserted in the flow bore. Moreover, a seal ring is fitted over the shaft to avoid the liquid material from leaking toward a control mechanism that is a drive source for the shaft.
Accordingly, the liquid material stored in the syringe is in such a state that the flow passage being present inside the distributor and leading to the discharge port of the nozzle is fully filled with the liquid material.
In relation to the discharge device constituted as described above, it is known that, if air bubbles exist within the flow passage, an amount of the liquid material discharged from the device may vary. Furthermore, if air bubbles are mixed into the liquid material at the start of use, the mixed air bubbles are difficult to expel out, and accurate discharge is impeded. More specifically, discharge failures may occur; namely, the air bubbles are discharged during the discharge and the liquid material is not discharged, or a droplet is not formed even when the liquid material is discharged. For that reason, it has been usual so far to perform a centrifugal debubbling process or a vacuum debubbling process on the reservoir (syringe) filled with the liquid material, and then to mount the reservoir to a body of the discharge device.
In a discharge device of ink jet type, there also arises a problem with mixing of air bubbles. More specifically, if air bubbles are mixed into ink, pressure of an expanding bubble generated due to heating and providing ink discharge energy, or pressure of a driver for pushing the ink is not appropriately transmitted to the nozzle. Hence a failure in ink discharge from a head nozzle tends to occur. To cope with the above problem, Patent Document 2 proposes a liquid filling method of placing a work inside a chamber of an airtight structure, reducing pressure in the chamber to a level close to a vacuum, and filling a fixed amount of liquid into the work by differential pressure between the vacuum pressure in the chamber and the atmospheric pressure in a supply tank where the liquid is stored.